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Spin-orbit coupling links spin and momentum degrees of freedom by the Hamiltonian H = ξLS (L, S: orbital momentum and spin operators, ξ: coupling strength). It is the origin of phenomena such as magnetocrystalline anisotropy and anisotropic magnetoresistance, which are of fundamental interest and important for sensor applications. To tune spin-orbit coupling at a single atom, the high rotational symmetry of the atom should be reduced. Johannes Schöneberg, Alexander Weismann and Richard Berndt achieved this by constructing dimers from single Pb atoms on an Fe double layer substrate, whose domain pattern exhibits suitable magnetization directions. First-principles calculations by Paolo Ferriani and Stefan Heinze reveal the molecular orbitals that cause the large observed anisotropic magnetoresistance. The results are published in Physical Review B "Tunneling anisotropic magnetoresistance via molecular Pi orbitals of Pb dimers" and have been highlighted by an Editors' suggestion for papers that the editors and referees find of particular interest, importance, or clarity.

Plenty of publications report on the conductance of molecular wires between electrodes. Characterization of the junction geometry, however, is usually missing. We synthesized a molecule for low-temperature STM experiments that stands vertically on a substrate. Despite this reductionist approach, its conductance data turned out to be
complex. Calculations show that geometrical changes, orbital symmetries, and bond formation control the conductance. This joint work within SFB677 by
Torben Jasper-Tönnies, Aran Garcia-Lekue, Thomas Frederiksen, Sandra Ulrich, Rainer Herges, and Richard Berndt has recently been published in Physical Review Letters and highlighted as Editors' Selection.

Cooperation with successful postdoc of SFB 677 continues at international level

10.01.2017

Although Yong-Feng Wang left Kiel University five years ago the cooperation with the colleagues from the SFB 677 and the group of Professor Richard Berndt at the Institute of Experimental and Applied Physics still continues. Most recently a joint paper about the vacuum synthesis was published as a cover story of the journal Chemical Communications. Since 2006 Wang worked as a postdoc in the group of Professor Berndt and was involved in numerous publications. 2012 Wang went to Peking University, by now he leads a group at the Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics himself.

In their paper the international group of scientists present tunneling microscopy and spectroscopy data from magnetic magnetic aluminum phthalocyanine (AlPc) which was prepared in ultrahigh vacuum using on-surface metalation from H2Pc. It turns out that AlPc remains paramagnetic on Au(111) with its spin density distributed over the isoindole lobes. “The vacuum synthesis is a powerful method to synthesize air-unstable molecules like the magnetic AlPc molecules we synthesised in our paper”, Wang explains. “In vacuum, the effect by air reactive molecules such as oxygen and water can be excluded.”

“Results like these show how international successful the early career scientists of our Collaborative Research Center are. I am very glad the cooperation with Yong-Feng Wang continues despite the distance between Peking and Kiel”, says Richard Berndt. “My time in Kiel was the most important period in my scientific career“, Wang sums up. “Here I learnt how to find important scientific questions, how to solve them, how to make high-quality scientific figures, and how to write high-level papers.” Since he left Kiel Wang came back for two longer research stays to work with Berndt again. In future, he hopes to set up an international cooperative lab to continue their collaborative work.

During the recent meeting of the condensed matter division of the German Physical Society Dr. Manuel Gruber successfully competed for the PhD thesis prize of the magnetism division (ThyssenKrupp Electrical Steel PhD prize).

Manuel carried out his pioneering studies at the Karlsruhe Institute of Technology with Prof. Wulfhekel and the University of Strasbourg with Dr. Beaurepaire. He explored the impact of molecules on the magnetic properties of inorganic substrates as well as the possibility to switch the magnetization of individual molecules adsorbed on surfaces. As a postdoc with Prof. Berndt he is presently working on related topics within SFB 677.

Making a switchable magnet from a biomolecule

18.01.2016

A molecule is magnetic (more precisely: paramagnetic) when its number of electrons is odd or when it contains transition metal ions like iron. Sujoy Karan from the group of Prof. Berndt investigated all-trans-retinoic acid, a non-magnetic bio-molecule with an even number of electrons, on an inert gold surface and observed that, surprisingly, the molecule may be made magnetic by passing current through it. Once it is magnetic, it may be switched back to non-magnetic. This process may be repeated and does not affect neighboring molecules.

Currently, these observations are a serious challenge to state-of-the-art theory. From a broader perspective, they suggest that it may be possible to custom-make arbitrary arrays of ultrasmall magnets on surfaces using an unforeseen class of molecules. In addition, living organisms utilize retinoic acid for signal transduction. Whether effects related to the new observation may play a role in organisms is yet unknown.

First single molecule potentiometer

03.07.2015

Interpreting electron transport through molecular junctions lies in the broad interest of understanding nanoscale junctions, which are sensitive to both physical and chemical parameters.

In a Letter recently published in Physical Review, Sujoy Karan, and colleagues from the group of Professor Richard Berndt, the Max-Planck-Institut für Mikrostrukturphysik and the Universities of Hamburg and Würzburg report how the electrostatic potential is distributed across a junction comprising single molecules coupled to macroscopic electrodes.

Contacting a porphyrin molecule on gold in a low-temperature scanning tunneling microscope, they showed a way to utilize a sharp spectral feature to obtain information on the local potential of the molecule.

Noise in electronic circuits is an inevitable nuisance. How does it change when a circuit is scaled down to the ultimate limit of a single atom?

In a recent publication in Physical Review Letters Andreas Burtzlaff, Alexander Weismann and Richard Berndt together with Mads Brandbyge from the Technical University of Denmark report the first experimental data on the shot noise of the current through single magnetic atoms. The noise turns out to be surprisingly low. The sophisticated measurements are complemented by state-of-the-art transport calculations and reveal that the electron spin plays a crucial role in lowering the noise level. The article has been highlighted by an Editors' Suggestion.

The idea of the experiments in layman's terms:

The way electrons move through a single atom contact is similar to a crowd of people passing through a revolving door. When such a door works smoothly people leave it at a constant rate. This corresponds to electrons passing through a fully open quantum transport channel of the atom. However, it may happen that a channel randomly reflects some of the electrons that are coming in. This is analogous to a door that occasionally gets stuck. The resulting irregularities of the flows of people or electrons thus provide an extra piece of information about the door or the atomic channel. In the case of electrons, the randomness leads to noise of the current which may be amplified to become audible.

The experiment adds another twist by having different channels for opposite spin orientations of the electrons. This is comparable to having separate doors for, e. g., men and women. The noise of the electron current reveals that the transmission through magnetic atoms depends on the electron spin. This corresponds to men and women getting stuck in their respective doors with different probabilities. The former information will be useful in better understanding spin transport at the ultimate limit of miniaturization. The latter probably suggests that it's time to call a mechanic.

Best Poster Prize for Dr. Nadine Hauptmann

26.01.2015

Dr. Nadine Hauptmann was awarded with a best poster prize for her presentation entitled "Force and conductance in molecular junctions" at the 543th Wilhelm and Else Heraeus Seminar in Bad Honnef. Under the topic "Electron Transport through Atoms, Molecules and Nanowires: Advances in Theory and Experiments", the seminar brought together around 70 experts of this research field. Dr. Nadine Hauptmann is a post-doc in Professor Richard Berndt's group and works on forces and transport properties of single molecules using a combined low-temperature scanning tunneling and atomic force microscope.

A fresh look at Bucky Bulbs

26.01.2015

The interaction of light and molecular junctions between metallic surfaces is a challenging topic bridging nanoelectronics and plasmonics. In a recent publication in Physical Review Letters Natalia L. Schneider and Richard Berndt together with their colleagues Jintao Lü and Mads Brandbyge from the Technical University of Denmark report the first investigation of light emission from a single molecule junction in the limit of strong coupling of the molecule to the metallic leads. The light emission is used to probe quantum shot noise and charge fluctuations at the biased junction. The new insight provided by the experimental technique and the theoretical approach have been highlighted by an Editors' Suggestion.

Plasmonic remote control

26.01.2015

Plasmonics - controlling and using light in nanostructures - is currently among the hottest topics in condensed matter physics. In a recent article Natalia L. Schneider and Richard Berndt show

that nanoscale plasmons may be used to remotely excite molecules to fluoresce. The plasmons in turn are excited by an electrical current, which makes the experimental approach particularly attractive as no background light is involved.

Switching of a tin-phthalocyanine: Current and Force

26.01.2015

A poster prize has been awarded to Nadine Hauptmann at the 15th International Conference on non-contact Atomic Force Microscopy 2012 in Cesky Krumlov (Czech Republic). The prize was sponsored by the company Specs for an excellent poster presentation and outstanding research topic. The conference was devoted to the latest progress in dynamical atomic force microscopy and brought together 200 scientists from all around the world. Nadine is currently working on her Ph.D. in Prof. Berndt's group. Within her Ph.D. project she investigates molecular switches using combined STM and AFM m easurements. Her topic is a key subject in the SFB 677 "Function by switching". In particular, her work focuses on the acting forces when contacting the molecules with a metal electrode.

Controlling spin-crossover of a single molecule

26.01.2015

For using single molecules as building blocks in spin-electronics (spintronics) it is important to be able to manipulate their spin state. In metal-organic complexes this is achieved by co-ordinating ligands to a metal centre, which leads to ligand-induced spin switching (LISS). Alternatively, spin crossover (SCO) complexes may be used, whose spin state may be controlled by temperature, light, pressure or magnetic fields. In contrast to LISS, SCO does not require chemical changes of the molecule. While the SCO effect has long been know from bulk materials control of the spin state of single SCO molecule has now been demonstrated for the first time by Gopakumar et al. By injecting electrons into selected molecules the IEAP researchers switched molecules between states with low or high spin. The work has been performed in a collaboration of the Tuczek and Berndt groups with funding through SFB 677. It has been selected as a Hot Paper in Angewandte Chemie.

Controlled metalation of single phthalocyanine molecules

23.01.2015

At the 22th Edgar Lüscher Seminar, in Klosters, Switzerland, Alexander Sperl was awarded a prize for his poster presentation. The meeting covers various aspects of modern physics. Alexander presented the controlled metalation of a single phthalocyanine molecule with the tip of a scanning tunneling microscope. He is currently working towards his Ph.D. in Professor Berndt's group. His research is focussed on single molecule chemistry, which is a key subject of the Sonderforschungsbereich SFB 677.

Poster Prize for Alexander Sperl

23.01.2015

At the 21th Edgar Lüscher Seminar, in Klosters, Switzerland, Alexander Sperl was awarded a prize for his poster presentation. The meeting covers various currents aspects of solid state physics. Alexander presented an optimized analysis procedure for scanning tunneling spectroscopy data. He is currently is working towards his Ph.D. in Professor Berndt's group. His research is focussed on single molecule chemistry using low-temperature STM.

November 2010

23.01.2015

At the joined conferences 5th Symposium on Vacuum based Science and Technology (SVST) and 16. Arbeitstagung Angewandte Oberflächenanalytik (AOFA16), in Kaiserslautern, Christian Hamann was awarded a best

poster prize, which is comprised of a certificate and prize money.

Electrospray deposition in ultra-high vacuum is an appealing approach for depositing fragile or non-volatile organic substances on surfaces. Mass selectivity, obtained by a quadrupole mass spectrometer, is particularly important for those materials and enables removal of molecular fragments and solvents or other impurities. Christian is currently doing his doctorate in Prof. Berndt's goup. Within his Ph.D. project, he designed a new electrospray deposition apparatus. This instrument is adapted to a cryogenic combined scanning tunnelling and atomic force microscope system.

Chemical Reactivity of graphene

23.01.2015

Graphene is a two-dimensional form of carbon with unique electronic properties, which make it the most lively field of condensed matter research. In his Ph.D. project in Professor Berndt's group, Simon Altenburg is investigating Graphene layers on metal surfaces. He discovered that the chemical reactivity of graphene on a metal substrate varies in a regular fashion on a nanometer scale. This opens interesting perspectives for creating regular arrays on graphene.

At the 11th edition of TNT, Trends in Nanotechnology<>, in Braga, Portugal, this work was selected for the best poster prize of the French research network GNT. The prize is comprised of a certificate and prize money. TNT is organized by Phantoms Foundation. The conference brought together 290 scientists from all around the world, who are working on various aspects of nanoscience and nanotechnology.

Noise from a Single-Atom Contact

23.01.2015

At the 11th edition of TNT, Trends in Nanotechnology, in Braga, Portugal, Natalia Schneider was awarded the best poster prize, which is comprised of a certificate and prize money. Natalia is investigating ultrasmall conductors: single metal atoms sandwiched between two electrodes. Her experiments showed that electrons flowing through a single atom generate high-frequency noise, which causes the emission of visible light. This noise may be partially suppressed by tuning the resistance of the conductor. Natalia is working towards her Ph.D. in Professor Berndt's group. She performed many of the experiments together with Dr. Guillaume Schull, CNRS Strasbourg. The workshop was organized by Phantoms Foundation. It brought together 290 scientists from all around the world, who are working on various aspects of nanoscience and nanotechnology.

Atomic-Scale Control of Electron Transport through Single Molecules

23.01.2015

In the most recent issue of Physical Review Letters, the Berndt group reports on the first successful experiment demonstrating control of the electron pathways through a single molecule. The article is being featured by the American Physical Society by a synopsis in "Physics - Spotlighting exceptional research". The article is also been selected for an "Editors' Suggestion".

November 2009

22.01.2015

In the most recent issue of Physical Review Letters, the Berndt group reports on the first controlled molecule-molecule contact.

The article is being featured on the cover of this issue. It is further discussed in a Physical Review Focus story and has been selected for Editors' Suggestions.

In the latest issue of Nature Chemistry, Nongjian Tao from Arizona State University highlights a publication by a team from the IEAP -Dr. Yongfeng Wang, Dr. J. Kröger, Prof. R. Berndt- in collaboration with Prof. W. A. Hofer from the University of Liverpool. Wang et al. recently reported in the Journal of the American Chemical Society on a breakthrough in molecular electronics: In a metal complex, a tin ion is pushed and pulled through a flat macrocyclic ring with a scanning tunnelling microscope, allowing the molecule to act as a switch. Nongjian Tao, Nature Chemistry, "Molecular switches: Pushing the right button", doi:10.1038/nchem.194

Best Poster Prize for Natalia Schneider

22.01.2015

At the workshop on Molecular and Organic Electronics: Bridging the Gap Natalia Schneider was awarded the best poster prize, which is comprised of a certificate and prize money. Natalia is currently working on her diploma project in Professor Berndt's group. Together with Dr. Guillaume Schull, a postdoctoral fellow, who joined the group in 2006 after his PhD at CEA Saclay, she is looking at the light which is emitted from a single metal atom sandwiched between two electrodes. "This is a new experimental approach which I hope will lead to fundamental insights into the transport of electrons which are confined to single atom or single molecule structures" says Natalia Schneider.

The workshop, which took place at the Physikzentrum Bad Honnef, 26 - 29 January 2009, was organized by Professors Saw-Wai Hla (Ohio University, Athens, Ohio, USA), Jürgen Rabe, Norbert Koch (both Humboldt University, Berlin, Germany) and Mark Ratner (Northwestern University, Evanston, IL, USA) and supported by the Wilhelm und Else Heraeus Foundation. It brought together an group of some 70 scientists from Europe, Israel, the US and Japan, who are working on various aspects of molecular nanoscience.

The confinement of electrons to regions so small that quantum effects are observed is compelling for applications in quantum computing, microchip fabrication, and nanoscale laser fabrication. Such nanostructures are typically studied with scanning probes like STM (scanning tunneling microscopy) or AFM (atomic force microscopy). Reporting in Physical Review Letters, Guillaume Schull, Michael Becker, and Richard Berndt of the University of Kiel have now combined the spectroscopic utility of optical probes with the atomic resolution of STM to create detailed images of electrons corralled into nanoscale metal islands on a gold surface. The researchers used tungsten tips to scan a chemically etched gold surface and collected photons excited by the tunneling current at the junction between the tip and the metal. The light, which was produced by the collective electron oscillations in the metal, called plasmons, was routed through an optical fiber to a spectrometer to create maps of photon energy as a function of position on the surface. These maps show striking variations caused by standing electron waves on the surface structures. In one case, the authors scanned over a triangular metal island and saw undulations in the electron density of states caused by quantum interference effects. In addition to the spatial map of quantum confinement, the spectral data show evidence of inelastic tunneling between the tip and the two-dimensional electron gas at the surface. This ability to examine the detailed physics of plasmonic photon generation at the atomic scale should be valuable in probing the optical properties of electrons confined to nanostructures. - David Voss

Controlled Contact to a C60 Molecule

Controlled Contact to a C60 Molecule Constant current scanning tunneling microscopy image of C60 molecules adsorbed on a copper surface. The molecules are arranged in a hexagonal lattice, with bright and dark rows located at different adsorption sites on the copper.